Process for the manufacture of krypton and xenon by separation from atmospheric air



Dec. 7, 1937. A. wen.

PROCESS FOR THE MANUFACTURE OF KRYPTON AND XENON BY SEPARATION FROM ATMOSPHERIC AIR Filed March 5, 1957 ATTORN EYS Patented pee. 7, 1931 PROCESS FOR THE ,MANUFACTURE OF KRYPTON AND. XENON BY SEPARATION FROM ATMOSPHERIC AIR Andi- Weil, Paris, France, assignor to Air Reduction Company, ,Incorporated, New York, N. Y., a corporation of New York Application March 5, 1937, Serial No. 129,139 In li'rance March 12, 1936 5 Claims. (01. 622-4755) A known process for obtaining from-the atmosphere the krypton contained therein (it should be understood that the term krypton here and hereafter designates the mixture of the krypton and the xenon contained in air)v consists in cooling this air down to the neighbourhood of its condensation point, rectifying it with a liquefied gas more volatile than krypton, then concentrating in krypton by vaporization and rectification the liquid resulting from the rectification of the air. Oxygen, nitrogen, or a mixture of both have already been mentioned as liquefied gases more volatile than krypton. For all the quantities of these liquefied gases which are in practice sufiicient for taking up the krypton contained in the treated air, the composition of the liquid resulting from the washing is the same as that of the liquid mixture of oxygen and nitrogen which is in phase equilibrium with the gaseous air. Under atmospheric pressure, this composition is, as known, about 50% of oxygen and 50% of nitrogen. Thus, whichever the initial composition of the washing liquid may be, that is, whether this liquid a consists of pure nitrogen, pure oxygen or a mixture of both, the liquid resulting from the washing contains about 50% of oxygen when the washing takes place under atmospheric pressure. For simplicityfs sake, this liquid will hereinafter be called 50%-oxygen liquid.

It has further already been proposed to carry out the vaporization of this 50%-oxygen liquid by putting it in heat exchange with a substantially equivalent quantity of a cold gas under a suitable pressure, which liquefies as the 50%- oxygen liquid vaporizes, and totake the liquid resulting from the liquefaction oi the cold gas as liquefied gas for rectifying the air. It has in particular been proposed to take as cold gas-a portion of the treated air, this portion being compressed with heatexchange between the air to be compressed and the air once compressed.

It has finally been proposed, for concentrating in krypton, by vaporization and rectification, the liquid resulting from the rectification of the air, to add to" the air to be treated the gas resulting from the nearly complete vaporization of this liquid, so as to retain the krypton carried along by this gas simultaneously with that of the treated air.

In the process of thisinvention the gas resulting from the vaporization of the 50%-oxygen liquid resulting from the washing of air with a liquid mixture of oxygen and nitrogen is rectified with liquid oxygen, liquid nitrogen or a mixture thereof separately from the air so as to free it from its krypton,'compressed, liquefied by heat exchange with the liquid mixture of oxygen and nitrogen to be vaporized, and the liquid thus formed is...utilized as washing liquid for the air to be treated. In this process energy is spared comparatively to the known process above referred to, in which the gas to be compressed consists of air.

The process of the invention may'be applied partially only, that is, one may rectify only a portion of the gas resulting from the vaporization of the 50%-oxygen liquid separatelyfrom the air to be freed from its krypton, or only a portion of the air separately from this gas, or

' constitute and separately rectify two mixtures of different oxygen contents, each of which comprises a portion of the air and a portion of the 50%-oxygen gas, and the richer of which in oxygen will be compressed and liquefied after having been rectified. In these manners of carrying out the process of the invention, care must separately from each other.

be taken, by adding to one of the two gases which have been subjected to" separate rectifications a portion of the other gas, or partially intermix-- ing them, that the gas which is liquefied be in a quantity approximating that of the 50%-oxygen liquid to be vaporized. But the advantages of the process are greatest when the whole of the 50%-oxygen gas and the whole of the air to be freed from its krypton are rectified entirely Therefore, when not otherwise stated, it is this case only which will be examined hereinafter- In order to rectify the 50%-oxygen gas resulting from the vaporization of the 50%-oxygen liquid, it is'of advantage to wash this gas with a portion of the 50%-oxygen liquid which has been formed by heat exchange of the compressed fying the %-oxygen gas is, like that resulting from the washing of the air, concentrated in krypton by vaporization and rectification. For this purpose, it is preferably added to the liquid resulting from the washing of this air, the mixture thus formed is nearly wholly vaporized, and the vaporized mixture subjected to rectification.

In order to carry out the vaporization of the liquid to be vaporized by heat exchange with the heating gas, the gas in the course of liquefaction and the liquid in the course of vaporization may be circulated in counter-current to each other, while causing the gas in the course of liquefactionto carry along the liquid condensed therefrom, and in the same way, the liquid in the course of vaporization to be carried along by the gas vaporized therefrom. In this manner of operation, whichsatisfies the ideal conditions of reversibility, the gas in the course of liquefaction may flow either downwards or upwards, or both the liquid in the course of vaporization and the gas in the course of liquefaction may fiow horizontally, one inside the tubes of a, nest of tubes disposed horizontally, the other outside these tubes.

The appended figure shows by way of example a mannerof carrying out the process in which, for concentrating in krypton by vaporization and rectification the %--oxygen liquid resulting from the rectification of the air, this liquid is nearly wholly vaporized and the vaporized gas is rectified by a portion of the krypton-free 50%- oxygen liquid which has been formed by heat exchange of the compressed 50%-oxygen gas with the liquid to be vaporized and has not been then utilized for washing the air to be treated. In this figure the following letters respectively show:

--A1 and A; a pair of regenerators alternately operated and utilized for cooling the air before it,is washed and warming it up after it has been washed,

B an expansion machine, in which cold is generated by the expansion of the air,

-C a rectification column in which the washing of theair from which the krypton is to be extracted takes place.

The 50%-oxygen liquid collected at the bottom of the column C is delivered to thevaporizer D which consists of a nest of tubes inside which the mixture of the liquid in the course of vaporization and of the gas vaporized therefrom circulates downwardly. The gas resulting from the nearly complete vaporization of the liquid is passed through the pipe N to the rectification column D. The gas leaving this column D at its top flows through the exchanger-liquefier G, the exchanger F, the compressor E and again the exchanger F. It is then divided into two parts. One, the larger, flows through the expansion machine H, in which it is expanded, with generation of cold, to an intermediate pressure enabling its liquefaction by heat exchange with the liquid to bevaporized. It then circulates upwardly, in admixture with the liquid condensed from itself, in the narrow spaces I between the tubes. The other part of the compressed gas passes through the exchangerliquefier G, in which it is liquefied by heat exchange with the cold air to be compressed, thus producing the necessary make-up liquid. A part, for instance of the liquid formed on the condensing side I of the condenser-vaporizer ID, is delivered through pipe P to the top of the column D; after having flown downwardly through this column it is added by means of the pipe 0 to the liquid coming from the column C; the remaining portion, say of the liquid formed in the condenser I is delivered to the top of the column C.

The small quantity of krypton-rich liquid remaining at the bottom of the vaporizer D as the result of the nearly complete vaporization effected in the vaporizer is delivered to the rectification column K heated at its bottom by means of the coil L and in which it is further enriched in krypton. The gas vaporized in this column is added, by means of the pipe M, to the gas flowing from the vaporizer D, whereas a small quantity of krypton-rich liquid oxygen is tapped from the column as the final result of the operation.

This small quantity of liquid is withdrawn from the mixture of nitrogen and oxygen which flows in a closed cycle along the path CDD'G-- F-E--F--HI. On the other hand, it is not the whole but only a portion of the liquid delivered at the top of the rectification column C which reaches the bottom of this column, on account of the unavoidable leakage of heat through the walls of the column, which entails the partial vaporizationof the downflowing liquid. These losses of liquid must be made up for. For this purpose, either liquid is allowed to form in the expansion turbine B as a result of the expansion or a small portion of the air which has been washed or is about to be washed is added to the mixture which flows along the aforementioned path. In the figure it is a small portion of the washed air which is added by means of the pipe Q. Instead of so operating, additional air which would not have flown through the regenerators A1 and A: could be introduced into the said path; its quantity could be larger than that tapped at the bottom of K, the excess air being passed through the regenerators A1 and A2 so as to facilitate the removal of carbon dioxide therein.

When starting the plant, as50%-oxygen liquid is generally not available, the path G--FE-F HID' is fed with air withdrawn from that which is about to flow or has just flown through the column C. This withdrawal for instance takes place by means of the above mentioned pipe Q. In proportion as liquid is formed in the liquefier G and thecondenser I, the opening of the valve of I the pipe Q is throttled and the washing liquid primitively consisting of a liquid the composition of which approximates that of air, becomes progressively richer in oxygen.

If, instead of directly washing, as in the appended figure, the50%-oxygen gas to be rectified with a portion of the 50%-oxygen liquid, the washing liquid was indirectly formed by an indirect contact, taking place in a condenser, between the gas to be rectified and the whole or part of the 50%-oxygen liquid, the gas resulting from the vaporization, carried out in the condenser, of the 50%-oxygen liquid should be added to the gas flowing through the plant. If the 50%-oxygen liquid is krypton-free liquid which has not been utilized for washing the air, the gas resulting from its vaporization is preferably added to the 50%-oxygen gas after the same has been rectified. If the 50%-oxygen liquid is a portion of the krypton-containing liquid which has just been utilized for washing the air, the gas resulting from its vaporization, carried out in the condenser, is preferably added, in order to avoid any loss of krypton, to the 50%-oxygen gas to be rectified.

As regards the apparatus FGH for forming the liquid with which the air is to be washed, it is to be noted that, Where the pressure prevailing in them is low, it is of advantage to replace the exchanger F by a pair of alternately'operated generators, to suppress the expansion machine H and to pass the whole or part of the cold compressed gas coming from these regenerators through an exchanger-liquefier in which it is cooled by the cold air which has just been washed in the column C. In this manner a portion of the compressed gas is liquefied in the exchanger-liquefier, the remaining portion being liquefied in the condenser-vaporizer ID.

0xygen may also be obtained when carrying out the process of this invention. For this purpose the 50%-oxygen liquid resulting from the rectification of the air, instead of being delivered appended figure, is admitted at an intermediate height of a rectification column of the common type, that is, no longer including the pipes N and O and the horizontal partition supporting the liquid flowing through the pipe 0. The vapors formed in the vaporizer of this column rise in the usual manner through the part of the column situated between the vaporizer and the place of delivery of the liquid, thereby rectifying the 50%-oxygen liquid and enriching it in oxygen. Gaseous oxygen is withdrawn 'in the vicinity of the vaporizer, preferably at a place separated by a few plates from the vaporizer, so as to be obtained as free from krypton as possible. When oxygen is thus withdrawn the exhaust gas escaping at the top of the column for rectifying the 50%-oxygen. gas is in a. quantity smaller than that of the liquid to be vaporZd: it is the quantity of this liquid less the quantity of the withdrawn oxygen. The oxygen must therefore be replaced by an equal quantity of another heating gas. A quantity of .cold air equal to that of the withdrawn oxygen is for instance put in heat exchange with the same, added to the air to be rectified in the column C, withdrawn from the air leaving this column and added to the aforementioned exhaust gas.

When the portion to be collected of the oxygen contained in the 50%-oxygen liquid resulting from the washing of the air is very small, for instance one-tenth or less of this oxygen, it is of advantage to keep the column D of the figure with its condenser-vaporizer as shown in the these columns being respectively operated as was hereinbefore described with reference to the column D-D' of the figure and the rectification column of the common type when these were successively assumed to be alone.

Nitrogen may also be obtained when carrying out the process of the invention. For this purpose, the liquid delivered at an intermediate height of the above mentioned rectification column of the common type which allows the obtention of oxygen is separated in this column into a first fraction, which is collected at the top of the column and consists of nitrogen, and a second fraction, which is collected near the vaporizer of the column and consists of a gas the richer in oxygen, the more nitrogen has been collected at the top of the column. A portion of this nitrogen, sufficient for taking up substantially all the krypton rising in the column,

its krypton by rectification, there is added a quantity of cold air equaltowhat of the nitrogen not recompressed, and the mixture thus constituted is compressed separately from the nitrogen, liquefied in the vaporizer of the rectification column and delivered in the liquid state to the top of the column for washing the air. The

' liquid to be vaporized will, in this case also, preferably be caused to flow in countercurrent to the gases to be liquefied. For this purpose, it will be sufficient to circulate both gases to be liquefied inside two separate nests of tubes.

Any portion of the oxygen-rich fraction collected near the vaporizer may also be removed from the plant simultaneously with the nitrogen, in which case there must be added to the portion not removed a quantity of cold air equal to that of the removed gases.

I claim:

1. A process for extracting krypton and xenon from atmospheric air by rectifying gaseous air with a liquid mixture of oxygen and nitrogen and vaporizing the liquid resulting from the rectification, wherein the gas resulting from the vaporization of the liquid mixture of oxygen and nitrogen resulting from the rectification is rectified with liquid oxygen, liquid nitrogen or a -mixture' thereof separately from the air so as to free it from its krypton, compressed, liquefied by heat exchange with the liquid mixture of oxygen and nitrogen to be vaporized, and the liquid thus formed is utilized as washing liquid for the air to be treated.

2. A process as set forth in claim 1, wherein the mixture of the liquid to be vaporized and of the gas resultingfrom the vaporization of this liquid flows in countercurrent to the mixture of the gas to be liquefied and of the liquid resulting from the liquefaction of this gas.

3. A process as set forth in claim 1, wherein a portion of the liquid resulting from the liquefaction of the compressed gas and which has, if desired, just been utilized for rectifying the a r, or air at its condensation temperature which is about to be or has just been rectified, are utilized as agents bringing about by direct or indirect contact the rectification of the gas resulting from the vaporization of the liquid resulting from the rectification of the air.

4. A process as set forth in claim 1, wherein the whole or part of the liquid which has been utilized for rectifying the air is separated by vaporization and rectification into oxygen, which is removed from the plant, and a gas richer than the liquid in nitrogen, a quantity of cold air equal to that of the removed oxygen is added to thegas richer than the liquid in nitrogen, and

the mixture thus constituted is utilized as gas, the

liquefaction of which, effected in heat exchange with the whole or part of the liquid to be vaporized, produces the whole or part of the liquid for rectifying the air to be treated.

5. A process as set forth in claim 1, wherein the liquid which has just been utilized for washing the air is separated by vaporization and restification into nitrogen, which is removed from the plant, and a gaseous fraction richer than this liquid in oxygen and which is withdrawn from the rectification column at a place separated by rectification plates from the vaporizer, a quantity of cold air equal to that of the removed nitrogen is added to this fraction, and the mixture thus constituted is utilized as gas the liquefaction of which, effected in heat exchange with the liquid to be vaporized, produces the 

